1. Field of the Invention
The present invention relates to a fluid clutch to be used in transferring driving torque of a driving disc to a case through an oil medium by which the oil is supplied to a torque-transfer chamber, more specifically related to a fluid clutch meant to act as a control of the rotational movement of a cooling fan for an automobile engine which is provided to a case. For more details, this invention relates to a temperature-sensitive type fluid clutch which has an automatic control function for an operation of a cooling fan utilized for an internal combustion engine that is supplied for vehicles in accordance to ambient temperature conditions.
2. Description of the Prior Art
As a fluid clutch device utilized for the aim of controlling a rotational movement of a cooling fan in an internal combustion engine for vehicles, it is a common method to transfer a driving torque of the driving disc through an oil medium that is supplied in the torque transfer chamber. In prior art structure of the fluid clutch mechanism, for example, a coupling device (fluid clutch) is described in Tokkosho 63-21048), in which the inside of a closed housing is divided into a torque transfer chamber and an off basin chamber by means of a partition plate. A driving disc is being disposed inside the torque transfer chamber in a rotatable manner through a driving movement of the driving portion, oil in the oil basin chamber is being supplied to the torque transfer chamber through a flow control hole which has been formed on the partition plate, and the oil in the torque transfer chamber is returned back to the oil basin chamber through a dam that has been provided on the inner peripheral wall of the closed housing being opposite to the driving disc and a circulatory path which has been connected to the dam. By utilizing the aforementioned type of a fluid clutch, a driving torque created on the driving disc will be successively transferred to a case through the oil that is supplied from the oil basin chamber to the torque transfer chamber and this in turn will cause the rotation of a fan disposed on the case, so that, for example, automobile engine can be cooled. Moreover, this type of the fluid clutch will act as an aid to detect an ambient temperature through a bimetal, so that when the temperature raises, an opening angle of the flow control hole is increased and this will lead to the increase of the amount of oil inside the torque transfer chamber, resulting in increasing the revolution of the case so that the fan will rotate at a consequently higher speed and this will enhance the cooling efficiency.
However, the foregoing types of a fluid clutch possess the following drawbacks. Namely, in cases when the engine starts with a large volume of oil inside the torque transfer chamber or when the engine accelerates rapidly, a case (or cooling fan) located on a driving side will be subjected to a rapid increase of revolution for a short period of time due to the presence of the large volume of oil inside the torque transfer chamber in accordance with an acceleration of the driving disc on the driving side. This phenomenon is called as "accompanying rotation" which represents in fact a number of disadvantages which are fan noise, discomfort accompanied by the fan noise, and reduction of the fuel efficiency.
The "accompanying rotation" phenomenon that takes place in a re-starting engine having the aforementioned conventional type of the fluid clutch will become of a much more effect if the oil mount in the torque transfer chamber is of a larger quantity. As a means to overcome the problem, as for example what has been disclosed in Tokkosho 63-21048, the oil flowing out from the flow control hole on the partition plate is being driven to get introduced momentarily to an opposite side along the diametral direction and then the oil is to be supplied to the torque transfer chamber.
According to the aforementioned structure, when the engine stops while there is almost no oil inside the torque transfer chamber and a plenty of oil is present inside the oil basin chamber, the "accompanying rotation" phenomenon would not take place among a re-starting of the engine since the oil would not flow from the off basin chamber into the torque transfer chamber. However, the foregoing structure can not prevent the "accompanying rotation" phenomenon in the cases when re-starting the engine while there is a large volume of oil inside the torque transfer chamber or the case when the engine is rapidly accelerated.
Hence, it is necessary to increase the exhausting capacity by the aforementioned dam so that the previously described excess oil remaining in the torque transfer chamber would be exhausted as soon as possible at a re-starting or rapid acceleration of the engine. The exhausting capacity that is meant to be given by the dam can be increased by changing a size, shape or number of the dam. However, since, according to the conventional type of the fluid clutch, the off supply to the torque transfer chamber is achieved only by a centrifugal force acting on the circulating oil inside the oil basin chamber, and this means that a large flow rate can not be achieved so that the oil supply capacity is low. This is considered to be a disadvantage. Therefore, even if by making use of the exhausting capacity supplied by the dam, the circulating amount of off is controlled by the supplying capacity, and this means that the oil level in the torque transfer chamber is under the required level and a desired fan rotation is not achieved. Moreover, under the circumstances when the circulating amount of oil is small, the remaining time of the oil between the torque transferring surfaces will become larger, causing the oil temperature to increase and an expected oil deterioration is more likely to occur due to the fact that the oil will absorb the thermal energy generated by the slipping due to the rotational differences between the case and the disc.